Page:ThomsonMagnetic1889.djvu/14

 Since $$\sin \beta=v/\omega$$, this expression vanishes unless $$\theta=\beta$$, when it becomes infinite, so that the magnetic force and the electric displacement seem confined to the surface of a cone of semi-vertical angle $$\beta$$, the vertex pointing in the direction of motion.

Trinity College, Cambridge,
 * April 24, 1889.